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Discussion Starter · #1 ·
Is there anything that can be done to improve the accuracy and/or consistency? Maybe a flash at the dealer? My economy and fuel used DIC numbers are usually off compared to actuals based on the fill up quantity and mileage driven. At every fill up I reset the #2 trip meter/fuel economy average and the fuel used quantity. Also at fill ups I enter mileage and fuel quantities into my phone app and then compare. The DIC is almost always 10-20% off - always on the optimistic side. (Although occasionally it is spot on). I know there is some variation due to fill up technique, pump differences, atmospheric conditions, etc, but the difference seems excessive. Yesterday I put 11.2 gallons in according to the pump but the DIC said I only had used 9.3. I think I am being very careful and consistent when filling up, but maybe some fill ups I'm not really getting it full?
 

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I'm not sure there is a way. Mine seems to be as much as 10% off at a fill up, but my lifetime mpg shows 33.0 mpg while my fuelly account shows 32.7. So, it seems to be real close for lifetime of the vehicle
 

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Make sure you use a level driveway filling station, most are, but sometimes they are sloped.
 

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The DIC in the North American gas Cruze under estimates the actual fuel used by 2 to 10%, resulting in a 2 to 10% optimism in the fuel economy numbers. This is actually a GM North America problem and not just with the Cruze. GM apparently got it right in the CTD.
 

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Miine always reads optimistic, I figured it was just not counting the fuel used to prime the car when starting, or some of it was evaporating or something.
 

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That circle with the line through it that accompanies the readout stands for 'Average'.

It is not intended to be, nor could it be, absolutely accurate.

The readout is based on math.....percentage of throttle opening/how long/ how many miles, etcetera. It does not actually measure fuel.

Rob
 

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My CTD is super close. when i look at fuel used when i fuel up the car will say 9.8 used and i will in actuallity used 9.1 or so
 

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The readout is based on math.....percentage of throttle opening/how long/ how many miles, etcetera.
I would have thought it would be based on commanded fuel injector pulse width. However, even then, it would have to have some way of converting it to "gallons". I doubt if the amount of fuel delivered is a linear function of the electric pulse. It takes time for it to open and close.
 

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Discussion Starter · #9 ·
That circle with the line through it that accompanies the readout stands for 'Average'.

It is not intended to be, nor could it be, absolutely accurate.

The readout is based on math.....percentage of throttle opening/how long/ how many miles, etcetera. It does not actually measure fuel.

Rob
I understand how averages and computing algorithms work - the actuals number I am calculating is also an average. The fact that it is always optimistic for me and virtually everyone else that reports on this issue points to the fact that there is an issue with the algorithm used to calculate these numbers. With the amount of computing power used to control our cars, it is not unrealistic to expect a fairly accurate report of quantity of fuel used over time. The computer knows how often and for how long it fired the injectors and it should be able to account for the amount of time it takes to open them since it would be fairly consistent over time. Heck, my '02 Dodge had way more accurate fuel economy reporting - consistently within 5%.

Thanks, everyone, for the replies. I think I will just have to learn to live with this annoyance - I love my Cruze in most other ways. I mostly now just want to find a way to make it more consistent so it reports the same amount of optimism every time. I am a little concerned with fill up differences - isn't there an issue with the baffles in an ECO's tank that can make it hard to get a truly full tank?
 

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I understand how averages and computing algorithms work - the actuals number I am calculating is also an average. The fact that it is always optimistic for me and virtually everyone else that reports on this issue points to the fact that there is an issue with the algorithm used to calculate these numbers. With the amount of computing power used to control our cars, it is not unrealistic to expect a fairly accurate report of quantity of fuel used over time. The computer knows how often and for how long it fired the injectors and it should be able to account for the amount of time it takes to open them since it would be fairly consistent over time. Heck, my '02 Dodge had way more accurate fuel economy reporting - consistently within 5%.

Thanks, everyone, for the replies. I think I will just have to learn to live with this annoyance - I love my Cruze in most other ways. I mostly now just want to find a way to make it more consistent so it reports the same amount of optimism every time. I am a little concerned with fill up differences - isn't there an issue with the baffles in an ECO's tank that can make it hard to get a truly full tank?
I agree, I think it wouldn't be that hard to report more realistic numbers. I just track it all on fuelly so I know how many miles I've driven over how many gallons I've bought.

Also, I don't have the eco tank and even I have not been able to get more than 13.8 gallons in the supposedly 15.6 gallon tank. Even after driving 20ish miles into the low fuel light.
 

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I understand how averages and computing algorithms work - the actuals number I am calculating is also an average. The fact that it is always optimistic for me and virtually everyone else that reports on this issue points to the fact that there is an issue with the algorithm used to calculate these numbers. With the amount of computing power used to control our cars, it is not unrealistic to expect a fairly accurate report of quantity of fuel used over time. The computer knows how often and for how long it fired the injectors and it should be able to account for the amount of time it takes to open them since it would be fairly consistent over time. Heck, my '02 Dodge had way more accurate fuel economy reporting - consistently within 5%.

Thanks, everyone, for the replies. I think I will just have to learn to live with this annoyance - I love my Cruze in most other ways. I mostly now just want to find a way to make it more consistent so it reports the same amount of optimism every time. I am a little concerned with fill up differences - isn't there an issue with the baffles in an ECO's tank that can make it hard to get a truly full tank?
The ECO MT has a shroud on the main tank vent that blocks air escape starting 3 gallons earlier. You can still fill past this if you want but for normal purposes this isn't needed.
 

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I monitor my fuel used on the DIC as I pull into the station, I typically aim for a consistent fill level of 1.0l beyond that number fill but just recently bumped it up to 1.5L I think that it will work it's way up to 2.0L. There are times that I hit the first click other times I have not, and the latter has been happening the last few tanks. I am only doing this to manage the MPG swings induced by fillups. when I go home an fill another 10L with a ventless gas jug, as indicated on my fuel log on Ecomodder.
 

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I have wondered about the tire pressure affecting the circumference of the wheel. Could the mileage actually be off?
 

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PART of the problem is "how long" the ECU operates the engine in "open-loop" mode -- while engine temperature is below 'normal'-- before it can switch into "closed-loop" operation. During that time, the engine is NOT operating at 14.7:1 AF-ratio, which is what the ECU is designed to operate at.
 
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PART of the problem is "how long" the ECU operates the engine in "open-loop" mode -- while engine temperature is below 'normal'-- before it can switch into "closed-loop" operation. During that time, the engine is NOT operating at 14.7:1 AF-ratio, which is what the ECU is designed to operate at.
They (well, the gassers) get into closed loop mode within 30-45 seconds of a cold start, though. I've had inaccurate all-highway, all-day driving tanks too.
 

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Discussion Starter · #16 ·
I have wondered about the tire pressure affecting the circumference of the wheel. Could the mileage actually be off?
Maybe, but it wouldn't explain my discrepancy even if so. Odometer shows x number of miles between fillups - if I divide by fuel amount I buy at the pump I get one MPG, if I divide by fuel used according to the DIC, I get another, much better number.

Thanks for the replies, everyone. Interesting to see others that have the same problem and their specifics.
 

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My lifetime DIC mpg is 31.1 mpg and according to fuelly it's 30.5. Similar to what others report. That's only about 2% optimistic which really isn't bad.
 
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